1. Field of the invention
The present invention concerns a novel granular material intended for use in public works, obtained through chemical processing on site or at a central station, of natural clay or alluvial soils, and relates to their method of processing as well as to the chemical compositions to be used for performing this processing operation.
Naturally available granular materials formed of sand and/or gravel do not present sufficient cohesion in the dry state when they contain substantial quantities of fines and, more specifically, of constituents the granulometry of which is comprised between 0.2 and 20 micrometers such as clays and alluvials. On the other hand, these natural binders lose their cohesion once they are soaked with water, and this therefore severely limits their conditions of use for the construction of works intended to be exposed to hydrological variations of the environment.
Usual solutions to overcome these problems have been known for many years, i.e. the use of materials free of clay or alluvial but to which have been added either organic, thermoplastic (tars, bitumens, polymers) or even thermo-hardening (synthetic resins) binders; these are morters and concretes of all kinds.
Another, less radical solution consists in using the materials, without their fines being separated, after their submission to a processing that confers to these materials an acceptable resistance to water. This is what can be considered as a stabilization.
These processing operations are based upon the reactivity of the clay based minerals with respect to various chemical compounds, the result being the constitution of modified clays the physical, chemical and geotechnical characteristics of which are specifically transformed. Processing operations which are based on aqueous solutions or powders are preferred, due to their simplicity and their economy. Among the chemical agents that can be used may be cited more particularly hydrophobating additives and hydrophilic colloids or gels.
Hydrophobating additives are essentially constituted by long hydrocarbon chain organic cations, such as fathy amines or quaternary ammonium derivatives comprising one or several chains comprising at least 12 carbon atoms. These products, such as stearylamine, or dimethyldistearylammonium chloride, used in very small quantities, modify in a spectacular manner the water-resistent quality of the clay or alluvial materials. (see for example J. M. HOOVER and D. T. DAVIDSON, Organic cationic chemical as stabilizing agent for Iowa Loess, Bul. N. 129, Highway Research Board, Chemical and mechanical stabilization).
But this action does not simultaneously lead to any real alteration on the natural cohesion of the soil, and the hydrophobated soil, after being soaked, does not have an improved bearing capacity over that of the same non-hydrophobated material.
Hydrosoluble organic polymers, among which can be cited the lignosulfites, the hydrolysed polyacrylamides, the polynaphtylmethanesulfonates, the carboxyalkylcelluloses, the natural rubbers, have been used for another of their properties, i.e. the flocculation of the natural clays. In roadmaking techniques, the improvement obtained is that of the consistency index, in fact an improved bearing capacity of the processed soil with respect to that of the natural soil, for an identical water content. These hydrophilic polymers do not, however, by themselves exert sufficient action so as to confer upon the natural materials the bearing capacity that is require to realized works exposed to severe weather conditions.
The applicants have observed that it was possible to obtain materials which were entirely suitable for their insensitivity to water and equally suitable for use in the construction of non-covered works, by applying to sands and/or clay and alluvial gravels a mixed processing operation, through hydrophilic polymer and cationic hydrophobating additives used in small quantities.
Natural soils that can be very substantially improved by such a mixed processing operation are for example, according to the classification used in the "Recommendation pour les Terrassements Routiers, Service d'Etudes Techniques des Routes et Autoroutes et Laboratoire Central des Ponts et Chaussees", January 1976, fine soils of categories A.sub.1 and A.sub.2 comprising slightly plastic alluvials, grits, sandy or gravelly soils with fines of category B, silty to very silty sands and gravels, clayly to very clayly sands and gravels; soils comprising fine and rough elements of category C, silex clays, millstone clays, scree, moraines, dry rocks and rough alluviums.
All these materials are classified as sensitive to water, their water-sensitivy being due to a very rapid reaction of their mechanical behaviour to the variations of their hydric and climatic environment.
One of the reagents of the invention is constituted by a substance or a mixture of substances, taken from among the group of cationic hydrophobating additives. Such products are found, in particular among:
the long chain fatty amines, having the general formula PA1 in which at least one of the R radicals is a hydrocarbonic chain, linear or branched, saturated or unsaturated, comprising from 10 to 24 carbon atoms, the other identical or different chains, when they are not chains of this type, are C.sub.1 to C.sub.4 short hydrocarbon radicals, or hydrogen, the preferred substances being primary monoalkylamines such as laurylamine, oleylamine, stearylamine in their pure or technical form such as coprah amine, tallow amine or hydrogenated tallow; PA1 hydrosoluble salts of these amines, for example chlorides, acetates, formiates; PA1 derivates of quaternary ammonium having the general formula: ##STR1## where at least one of the radicals R is a linear or branched, saturated or unsaturated hydrocarbon chain having from 10 to 24 carbon atoms; PA1 the lignosulfonates, PA1 the acrylic polymers, polyacrylates, polymethacrylates, hydrolysed polyacrylamides . . . , PA1 polyvinylic alcohols, PA1 alkylene oxide polymers and copolymers, PA1 modified celluloses, hydroxyalkylcelluloses, carboxyalkylcelluloses . . . , PA1 polysaccharides, guar gums, alginates, xanthane, carraghenan . . .
R.sub.1 R.sub.2 R.sub.3 N PA2 where the other radicals R, when they are not chains of this type, are C.sub.1 to C.sub.4 short hydrocarbon radicals, identical or different, PA2 where X.sup.- is an anion such as Cl.sup.-, Br.sup.- or SO.sub.4 CH.sub.3.sup.- ;
the preferred substances being dialkyldimethylammonium salts such as distearyldimethylammonium chloride in its pure form or technical form such as ditallowdimethylammonium chloride or di(hydrogenatedtallow)dimethylammonium.
The second reactant utilized in the invention, in synergic activity with the previous one, is constituted by a hydrophilic polymer, and more specifically by a neutral or anionic macromolecule. The existence of adsorption phenomena of such structures on clays are known; this adsorption is extremely different from the quasi-irreversible adsorption of monomer or polymer cationic compounds, and most obvious result is a flocculation, i.e. a mechanical aggregation of the particules that alters the texture of the material according to modes and mechanisms described for example by A. S. Michaels, "Aggregation of suspensions by polyelectrolytes" in Ind. Eng. Chem. 1954, 46, No.7, pp-1485 or B. K. G. Heng. "Interaction of clay minerals with organic polymers, some practical applications, in Clays and Clay Minerals", 1970, No.18, pp-357.
Such products are found, especially in a non-limitative manner among:
There is a wide choice available among the hydrophilic polymers, provided that their molecular weight is comprised between 20,000 and 5,000,000, the rule being that the acceptable minimum threshold for the molecular weight is that much lower as the polymer presents a more pronounced anionic character, for example 3,000,000 for a totally non-ionic hydroxyethylcellulose, and 30,000 for a carboxymethylcellulose the substitution degree of which is 0.9.
The obtention of improved materials through a mixed processing is not yet obvious per se. If it is in fact known to render a material insensitive to water through processing with a hydrophobating additive, it may be feared that the addition of a processing with a hydrophilic agent impair this effect. U.S. Pat. No. 2,981,162 is undoubtedly a unique description of such an association, but the incompatibility between the two reactants renders it compulsory to operate the processing in two separate phases, which considerably complicates the practical use of the system on the works site.
Furthermore, the correct running of work sites requires an application of such materials, natural or chemically modified, at an optimum water content which is delimited in a fairly narrow interval. This water content at the Proctor optimum, according to the operating mode of the Laboratoire Central des Ponts et Chaussees, No. S. C.-1-1966 (Dunod); is generally close to the natural water content of soils, and in any case, somewhat lower that the water content at which these soils can be worked with some ease. It is thus totally inappropriate to furnish these soils with supplementary quantities of water by processing solutions, the operation rendering the work site inoperative until through evaporation the water content has returned to the desired value. The effect will be that much more extreme as the incorporation of the hydrophilic polymers requires diluted solutions, if it is desired to avoid other difficulties due to the distribution or the spraying of solutions that are too viscous.
The applicants have found that it was furthermore particularly simple to obtain under ordinary work site conditions, materials intended for public works that are relatively insensitive or resistant to water according to the invention, by proceeding, prior to the definitive installation, to the mixing of the clay or alluvial soils with pulverent compositions consisting in a mixture of cationic hydrophobated additives and hydrophilic polymers, such as defined herein-above, and mineral powders. These mineral powders are advantageously selected from among the powders currently utilized in public works, and especially the fines obtained by grinding soft rocks (for example, non-crystalline limestones) or hard rocks (for example, silica, basalts, . . . ). Inexpensive fillers can be constituted by those that are separated from primary pounding sands and which are often neglected due to their very high content in cay compounds.
In a preferred form of the invention, mixed powder or dust compositions are used, obtained by hot spraying in a mixer of the cationic hydrophobated additive, in the molten form or in a concentrated solution, mixing and possibly regrinding, then mixing with a desired quantity of hydrophilic polymer itself present in powder or dust form. It is however obvious that any other method of preparation of the composition can be utilized.
In the processing compositions according to the invention the cationic hydrophobasing additive and the hydrophilic polymer are present in a 10/1 and 1/10 ratio by weight, and the cationic additive polymer mixture and mineral powder are present in a 2/1 to 1/50 ratio by weight.
The useful quantities are such that the final content of the materials treated according to the invention are from 0.1 to 10 grams of each of the cationic additive and hydrophilic polymer reactants per kilogram dry soil. Preference is given to final compositions containing about 1 gram cationic hydrophobating additive per kilogram of soil, the quantity of polymer being of the same value, but it has been observed that in the case of a soils with a high clay content, generally fairly difficult to treat with a single cationic treatment, satisfactory results are obtained by preferably increasing the polymer content. Orientation tests, such as given in the examples, allow the man skilled in the art to select very simply the formulations best adapted to the specificiting of the soil to be processed.
The following non-limitative examples will render the invention more clearly apparent.
Example I to V show more precisely the advantage of the cationic additive polymer association in order to develop the resistance or insensitivity to water of the initial soil. They illustrate the useful laboratory tests and furnish indications as to the manner to carry out the best choice of the components and their quantities.
The following examples illustrate the preferred choices according to the invention insofar as they utilize dust powderous additives.